The present invention relates to a ventilating arrangement for a shaping tool in which a plurality of sintered metal lamellas are inserted into a tool wall which bounds a shaping nest of the tool.
Ventilating arrangements of the above-mentioned general type are known in the art. In tools for injection molding or die casting, when plastic particles fill the shaping nest, the air which is displaced by the molten plastic entering the tool must be withdrawn from the tool in extremely short time. In the event if it has an opportunity to be condensed and heated to a certain degree during the filling process, the molding can suffer from discoloration and burning. Moreover, at locations where air pockets are formed in the tool, the molding obtains a pitted or rough outer surface or completely reproduces imperfect contours of the shaping nest. Further, the tool itself may suffer from premature wear.
Attempts have been made to avoid the above-mentioned effect which is detrimental to the injection molding process or the die casting process and is identified in the special literature as so-called Diesel effect. These attempts include roughening of the separation plate of the molds or provision of grooves so that the surfaces forming the separation plane are no longer gas-tight. In the cases when the shaping nest is located outside of the separation plane of the mold, it was known to insert a sintered lamellas in the wall of the shaping tool at the most dangerous locations, for example at the deepest point of a dome-shaped or hood-shaped shaping nest.
The above-described construction involves relatively great labor expenses. In addition to this, the sintered lamellas which are inserted into the mold and must be relatively small because of the strength requirements, are unable to evacuate the air entering the shaping nest during sufficiently short time.